In a heavy-bottomed stockpot, lightly heat the olive oil over medium heat. Add the onions and fennel and cook until translucent (very important not to let them brown), about 10 minutes, stirring occasionally. Then add fennel fronds, garlic and bay leaf and cook for 5 minutes. Add tomato paste and stir to coat the vegetables. Cook for 3 minutes. Deglaze the pan with the white wine and let cook until wine has mostly evaporated. Add the clam juice, saffron and crushed tomatoes and bring to a boil. Lower heat and let the broth simmer on low, uncovered, approximately 30 minutes. Season with parsley, crushed red pepper, salt and black pepper.

Heat a large sauté pan over medium-high heat and add 3 cups tomato-fennel broth and fish. Arrange the clams around the fish and cover, watching carefully that the broth doesn’t boil over the sides. When clams begin to open, add the mussels and squid and cover. Once the clams and mussels are fully cooked (all shells are open; discard any that have remained closed), arrange over prepared pasta, garnish with fennel fronds and lemons and serve.